Rheem is a good brand. There are limits on distance, elbows, and pipe size, but the new ones use smaller pipe and can go greater distance than my 10 year old one. My old one uses 4" ABS/PVC pipe, but I believe the new ones can use as small a 2" and run like 30'. You can do a search and get the precise numbers.

I am in the same boat and FWIW my research came up with Bradford White as a preferred unit. The 50 Gal is around $1000 and has a pretty good efficiency factor of .62 which qualified for a $50 rebate in Seattle. It use 3" PVC vents. Check the website for sizes and specs. www.bradfordwhite.com